Apparatus for production of substituted pyridines



D. E. BERGER Feb. 23, 1960 APPARATUS Foa PRODUCTION 0F SUBSTITUTED PYRIDINES original Filed April 30, 1954 5 Sheets-Sheet@ ATTORNEYS Feb. 23, 1960 D. E. BERGER APPARATUS FOR PRODUCTION OF SUBSTITUTED PYRIDINES Original Filed April 30, 1954 VENT 3 Sheets-Sheet 2 FROM ANH L NH3 STORAGE AQUA NH3 7 TO PROCESS INVENTOR. D. E. BERGER BY .L

RECYCLE Hao Feb. 23, 1960 D. E. BERGERA APPARATUS FOR PRODUCTION OF SUBSTITUTED PYRIDINES Original Filed April 30, 1954 3 Sheets-Sheet 3 m 2 m 0 m O O 8 6R .l n m A OW mw 5m .l m m N 0 O O 4M m ma. m T G N O w E .r m C R m W l 0 T m H m 0 W 9 m O 7. A 0 O 6 O 0 0 O O O 0 m w w w 6 5 4 3 2 o 92mm; mammun. mom 5 0 0 0 0 O Oy O 0 O O O 0 4 w 9 8 7 6 5 4 3 2 I TEMPERATURE 'E INVENTOR 4 11E. BERGER F/G.

BY g4 Arron/vars United States Patent O APPARATUS FOR PRODUCTION OF SUBSTI- TUTED PYRID Donald E. Berger, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware 2 Claims. (Cl. 23a- 263) This is a division of my application Serial No. 426,-

787, filed April 30, 1954, now Patent 2,825,630, for

Stream Composition Control by Differential Pressure.

The condensation of aldehydes and ketones, either saturated or unsaturated, and derivatives thereof with ammonia or its derivative to form substituted pyridines is one of the oldest organic reactions. See R. L. Frank et al., Journal of the American Chemical Society, 71, pages 2629 et seq. (August 1949), and R. L. Frank et al., Jour1 nal of the American Chemical Society, 68, pages 1368- 9 (July 1946).

One method for producing these substituted pyridine products is to react an aqueous solution of ammonia with an aldehyde, ketone or derivative thereof at elevated temperature and generally in the presence of a catalyst. I will refer to the aldehydes, ketones and derivatives thereof as carbonyl compounds throughout this discussion. This synthesis step requires an aqueous ammonia stream of 25 to 40 weight percent ammonia. When the ammonia concentration is too high, the excess ammonia leads to overloading of the recovery equipment. Too low ammonia concentration leads to low conversion or reaction efficiency because the carbonyl Will be incompletely converted or will be partially consumed by side reactions in the absence of some excess ammonia. As has been said, the synthesis can utilize ammonia solution in the concentration range from 25 to 40` weight percent but fluctuations Within this range will upset the process control. For best control and optimum conversion, it is desirable to operate in the narrow limits of 30 to 35 percent ammonia -concentration and to control the selected concentration within plus or minus 2 percent. With this strict cont-rol only minor surges in the process are encountered which are readily tolerated. Ammonia for this process is prepared by dissolving ammonia in water in an absorber. Three sources contribute arnmonia to the absorber, namely fresh anhydrous ammonia, recycle ammonia flashed from the reactor, and ammonia stripped from the product as will be seen from the detailed discussion of this invention. The last two named sources of ammonia are -subject to variations in the process and therefore a pre-set flow of anhydrous ammonia will lead to comparable variations in the ammo-nia concentration prepared in the absorber. While my invention is primarily concerned with controlling the ammonia concentration in aqueous solution for feeding a synthesis unit for producing pyridine derivatives by condensation of a carbonyl compound with ammonia, it will be obvious to those skilled in the art that the absorber and method of this invention can be used wherever aqueous ammonia is being prepared. When such a solution is prepared by adding anhydrous ammonia to water, such control is not especially required. This invention is particularly useful where aqueous ammonia is being prepared from a source of anhydrous ammonia in conjunction with one or more streams of ammonia of variable flow.

An object of this invention is to provide a method 2,926,074 Patented Feb. 23, i960 and apparatus for controlling the aqueous ammonia concentration in the synthesis of pyridine derivatives by condensingl a carbonyl compound with ammonia.

As has been said, this invention is particularly useful in the preparation of pyridine derivatives by the condensation of a carbonylcompound with ammonia and for that reason, I will further explain this invention in terms of such a reaction. As has been said, the condensation of a carbonyl compound with ammonia to form pyridine derivatives is one of the oldest in the art and no lengthy discussion is needed here. The carbonyl compounds are known in the art and illustrative examples are set -forth in detail in the above-named Frank et al. references. Some examples are acetaldehyde, crotonaldehyde, crotonaldehyde diethyl acetal, paraldehyde, benzalacetophenone, benzaldiacetophenone, ethylideneacetone, para-chlorobenzaldiacetophenone, and anisaldiacetophenone. Also mixtures of these materials may be used. These carbonyl products when condensed with ammonia yield a mixture of pyridines, however, by selecting a proper catalyst and condensation conditions, the yield will be primarily 2-methyl5ethylpyridine for the first four materials, 2,4,6-triphenylpyridine for/the next two, 2,4,6-collidine, 4(parachlorophenyl)-2,6di phenylpyridine, and 4-anisyl-2,6-diphenylpyridine for each of the others respectively.

Generally a catalyst is used, and I prefer a iluorine containing catalyst such as ammonium uoride, ammonium bifluoride, boron trifluoride, these preferably in a complex with ammonia or an amine; salts of iluorobon'c acid, salts of the lluorophosphoric acids, salts of tritiuoroacetic acid and salts of uosilicic acid. However, other catalysts known in the art can be used such as ammonium chloride, ammonium acetate, alumina, sul'fonic acids, etc.

The pyridine derivative made by the above process of great commercial importance at the present time is MEP (Z-methyl-S-ethylpyridine) which can be made by condensing paraldehyde with ammonia. MEP is useful as an intermediate in the production of MVP (Z-methyl- 5-vinylpyridine) which has a host of uses in polymerization processes. For that reason, I will further explain my invention by describing it in an MEP synthesis process wherein paraldehyde is condensed with ammonia to form MEP.

This invention can best be described by referring to the attached drawings of which:

Figure l is a flow diagram of an MEP synthesis process showing schematically how my invention is used in such a process,

Figure 2 is a schematic vertical section of the absorber and controls of my invention. The reference numerals are the same as used in Figure l for the same elements,

Figure 3 is a plot of ammonia concentration versus vapor'pressure at various temperatures, and,

FigureA is a plot of temperature against vapor pressure for various aqueous ammonia concentration.

Referring to Figure 1, paraldehyde from surge tank 1 is pumped at about 2000 pounds per square inch gauge (psig.) via pump 2 and conduit 3 to conduit 4 Where it joins a stream of aqueous ammonia which generally contains the condensation catalyst. The pressure must he suicient to maintain the reactants as a liquidphase under reaction conditions and can vary from about 850 psig. to over 2500 p.s.i.g. These reaction ingredients then pass to preheater 5 where the temperature is raised to 500 F. The temperatures generally used can range from 350 to 650 F. but are more commonly vbetween 450 and 550 F. The hot reaction ingredients pass via conduit 6 to reactor 7. The residence time in the reactor is approximately l5 minutes but contact time can vary from 5 minutes to several hours. The reactor 7 is di` vided into two zones A and B. In zone A, both burners and coolers are used to control the temperature since the reaction is slightly exothermic but requires high ternperature to proceed. In the zone B, only burners are used since the greater portion of the reactants will react in zone A so that zone B is used for additional residence time. The stream containing the reacted materials passes from reactor 7 via conduit 8, to pressure reducing wave 9 wherein the pressure is dropped to approximately 60 p.s.i.g. This reduction in pressure cools the stream to between Z50-300 F. and at the same time vaporizes most of the ammonia and part of the water. The stream is further cooled by means of cooler 10 and then passes to ash vessel 11. A large portion of the ammonia is flashed from the stream in this vessel and is removed through conduit 12.

The water, MEP formed in the reactor, dissolved ammonia and condensation byproducts pass via conduits `13 and 14 to stripper 15 wherein most of the remaining dissolved ammonia is driven off by heat through conduit 16. 'I'he organic and aqueous phases are passed via conduit 17 to vessel 18 where they are separated, the organic phase being removed via conduit 19. The water phase then passes via conduit 20 to stripper 21 wherein the last traces of ammonia and dissolved pyridines are removed via conduit 22 to accumulator 23. The water from stripper 21 is sent via conduit 24 to recycle water tank 25. Water, pyridines and ammonia from accumulater 23 are returned to the system via either conduits 26 and 27 to the ammonia ash vessel 11 or via conduits 26, 28 and 14 to the stripper 15.

Ammonia from ash vessel 11 and stripper 15 passes via conduits 12 and 16, respectively, to ammonia header conduit 29. Anhydrous ammonia from vessel 30 passes via conduits 31 and 32, ow control valve 33 and orifice 34 to said header conduit 29. The valves in conduits 31 and 32 are provided so that manual operation is possible, if desired, for example, when valve 33 is down for overhaul. The amount of ammonia passing to conduit 29 from ash vessel 11 and stripper 15 varies with operating conditions so in order to control the total ammonia passing to conduit 29, the ammonia from vessel 30 will have to` be varied to compensate for fluctuations from the other two sources. This is done by means of valve 33' as will be later shown. The ammonia from conduit 29 is introduced into the bottom of absorber 35. At the same time water from vessel 25 is introduced into the top of absorber 35 via conduit 36. The liquid level is controlled in absorber 35 by means of level controller 37 which actuates valve 38 in response to the level change admitting more or less water. When a soluble catalyst is being used the water from conduit 36 can pass to catalyst mixer 39 via conduit 40 where it dissolves the catalyst and returns to conduit 36 via conduit 41.

The desired temperature of the absorber is about 115 F. but it may be any temperature from 90 F. to 140 F. so long as the selected temperature is maintained reasonably constant. If the temperature in the absorberremains constant, then the pressure in vapor phase C above the liquid phase D will be dependent upon the concentration of ammonia in the liquid phase. However, since recycle water containing no ammonia is added continuously to the absorber, to obtain near equilibrium relations of the vapor and liquid phases, the liquid D is recirculated at a moderate rate by means of pump 42, cooler 44 and conduit 43. The cooler removes the heat of solution of ammonia in water and serves to maintain the absorber temperature at the desired level. A temperature controller 50 is operably connected by a temperature sensing element in conduit 43. This controller is also operably connected to valve 51 and admits more or less coolant to cooler 44 in response to changes in temperature of liquid in conduit 43.

A sealed bulb or cell 45 containing an aqueous solution of ammonia of a known concentration is inserted in the liquid phase of the absorber 35. The aqueous solution in bulb 45 will be at the same temperature as the surrounding liquid. This 4bulb is connected to differential pressure controller 47 via conduit 46. The differential pressure controller is also connected to the vapor zone of absorber 35 via conduit 48. This differential pressure controller is in turn operably connected to ow recorder controller 49 which is in turn operably connected to orice 34 and to control valve 33. The ilow recorder controller 49 is set to maintain a selected rate of fresh ammonia ow as measured by orifice 34, by proper positioning of valve 33. The selected flow rate can be varied in response to an air signal from differential pressure controller 47 which resets the selected rate. Therefore the rate of ow of ammonia through orifice 34 is controlled by the difference in pressure between the vapor pressure in the absorber and the vapor pressure of a known concentration of aqueous ammonia at the same temperature as the absorber. Since the known solution in bulb 45 is blended to have a concentration in the same range as desired in the absorber, only a small diEerential pressure will exist between it and the absorber pressure, and this will remain true in spite of temperature variations of the entire system. If a differential pressure does occur, it will be sensed and this control system will adjust the rate of fresh ammonia flow in the desired direction until a diierential pressure does not exist. The aqueous solution is withdrawn from the absorber via conduit 55 and passed to pump 54 where the pressure is raised to approximately 2,000 p.s.i.g. and from whence it is introduced to conduit 4 and is sent to the preheater 5 along with the paraldehyde from vessel 1.

The absorber is equipped with a pressure controller 52 which is operably connected to valve 53 and causes this valve to open to vent in case the pressure exceeds the safe limit for the vessel. Venting is normally required periodically to purge inert or insoluble gases from the absorber.

Figure 2 is an enlarged section of that part of Figure l showing the absorber 3'5 and the control apparatus. The numbers are the same as were used for the same elements in Figure l.

Referring to Figure 3, the total vapor pressure, in pounds per square inch absolute (p.s.i.a.), is plotted against the weight percent ammonia in aqueous solution at various temperatures. The slope of the curve between 30 and 40 weight percent ammonia in water at 115 F. is 2.5 p.s.i. change in vapor pressure for each percent change in composition. The system can tolerate a change of plus or minus 2 percent in composition which would be equivalent to plus or minus 5 p.s.i. change in pressure at F. The differential pressure controller 47 of Figures l and 2 should detect a change of plus or minus 1 p.s.i. or less and therefore the sensitivity of the apparatus is well within the tolerable composition limits.

Referring to Figure 4, the vapor pressure, in pounds per square inch absolute (p.s.i.a.), is plotted against temperature for various concentration of aqueous solutions. If it is desired to hold the ammonia concentration at 35 weight percent and 115 F. in the liquid phase in the absorber, there will be exerted 39 p.s.i.a. vapor pressure. Now, if the known solution in sealed bulb 45 (Figures l and 2) is 30 weight percent, the pressure in the bulb is approximately 28 p.s.i.a or a difference registered on the differential pressure controller of +11 p.s.i. In order to hold a liquid phase concentration of 35 weight percent, the differential pressure controller must be set for +11 p.s.i. differential. If the operating temperature level of the absorber changes to F., the solution in the sealed bulb 45 will then exert 37 p.s.i.a. vapor pressure and the desired +11 p.s.i. differential pressure will control the absorber so as to produce an aqua ammonia of 48 p.s.i.a vapor pressure at 130" F. corresponding to about 34 weight percent ammonia. This error arises from the slope of the vapor pressure versus composition curve (Figure 3) at 130 F., whose slope is about 3 p.s.i. per 1 percent ammonia. Similarly at 90 F. since the slope is about 1.5 p.s.i. per l percent, the aqua ammonia solution produced at +11 p.s.i. differential pressure will be 37.5 weight percent. The examples cited are extreme, since in practice the solution in the sealed bulb will be selected so that the differential pressure controller will need to be set to control at only a few pounds differential, not over or preferably a zero diiferential. Also the temperature will be controlled so as not to vary more than plus or minus 5 degrees and preferably plus or minus 2 degrees. Since the pressure in the bulb is the -base pressure, pressures above this are considered plus differentials.

I have described my invention in terms of one of its preferred embodiments. Those skilled in the art will see many modilications which can be made without departing from the scope of this invention. For example, it is within the skill of the art to supply the necessary valves, pressure regulators, pumps, relief valves and the like.

I claim:

l. An apparatus for condensing a carbonyl compound With aqueous ammonia, said apparatus comprising in combination a reaction vessel having an inlet and an outlet, means for applying heat and means for cooling said reaction vessel, pressure reducing means operably connected in said outlet means, means for separating unreacted ammonia from reactants, said separating means being connected into the outlet of said reaction vessel subsequent to said pressure reducing means, means for withdrawing thus separated ammonia, means for withdrawing the remaining reactants, means for separating thus withdrawn reactants into organic phase and water phase, an absorption vessel, means for introducing the withdrawn ammonia to a lower section of said absorption vessel, means for introducing water from said water phase to an upper section of said absorption vessel, means for detecting the liquid level in said absorption vessel, means for controlling ilow of water to said means for introducing water to said upper section of the absorption vessel, said control means being operably connected to said level detecting means and responsive to changes in liquid level in said absorption vessel, circulating means for withdrawing liquid from bottom section and introducing it into top section of said absorption vessel, means for regulating temperature of liquid being circulated by said circulating means, a cell containing an aqueous solution of ammonia of known concentration, said cell being disposed in said absorption vessel at a level below said liquid level, a differential pressure conrtoller, said diierential pressure controller being connected to said cell and to said absorption vessel above said liquid level so as to detect diEerence in vapor pressure between said cell and said absorption vessel, means for introducing make up ammonia into a bottom section of said absorption vessel, means for controlling the ow of make up ammonia through said means for introducing said make up ammonia, last said control means being operably connected to said dilerential pressure controller and being CII responsive to changes in pressure dierental, means for withdrawing aqueous ammonia from said absorption vessel, means for applying pressure to last said withdrawn aqueous ammonia, means for introducing carbonyl compound to the pressurized aqueous ammonia, and mean for introducing said aqueous ammonia and carbonyl compound to an inlet of said reaction vessel.

2. An apparatus for condensing a carbonyl compound with aqueous ammonia, said apparatus comprising in combination a reaction vessel having an inlet and an outiet, temperature control means in said reaction vessel, pressure reducing means operably connected in said outlet means, means for separating unreacted ammonia from reactants, said separating means being connected into the outlet of said reaction vessel subsequent to said pressure reducing means, means for withdrawing thus separated ammonia, means for withdrawing the remaining reactants, means for separating thus withdrawn reactants into organic phase and water phase, an 4absorption vessel, means for introducing the withdrawn arnmonia to a lower section of said absorption vessel, means for introducing water from said water phase to an upper section of said absorption vessel, means for detecting the liquid level in said absorption vessel, means for controlling ilow of water to said means for introducing water to said upper section of the absorption vessel, said control means being operably connected to said level detecting means and responsive to changes in liquid level in said absorption vessel, a cell containing an aqueous solution of ammonia of known concentration, said cell being disposed in said absorption vessel at a level below said liquid level, a diiferential pressure controller, said differential pressure controller being connected to said cell and to said absorption vessel above said liquid level so as to detect dilerence in vapor pressure between said cell and said absorption vessel., means for introducing make up rammonia into a bottom section of said absorption vessel, means for controlling the ow of make up ammonia through said means for introducing said make up ammonia, last said control means being operably c0n nected to said differential pressure controller and being responsive to changes in pressure differential, means for withdrawing aqueous ammonia from said absorption vessel, and means for introducing said aqueous ammonia and carbonyl compound to an inlet of said reaction vessel.

References Cited in the le of this patent UNITED STATES PATENTS 2,603,645 Hoog et al. July 15, 1952 2,615,022 Mahan Oct. 21, 1952 2,745,833 Stoops et al. May 15, 1956 2,766,248 Mahan et al. Oct. 9, 1956 2,775,596 Mahan Dec. 25, 1956 OTHER REFERENCES Perry: Chemical Engineers Handbook, 3rd ed., M Graw-Hill, New York, 1950, pp. 171-172. 

1. AN APPARATUS FOR CONDENSING A CARBONYL COMPOUND WITH AQUEOUS AMMONIA, SAID APPARATUS COMPRISING IN COMBINATION A REACTION VESSEL HAVING AN INLET AND AN OUTLET, MEANS FOR APPLYING HEAT AND MEANS FOR COOLING SAID REACTION VESSEL, PRESSURE REDUCING MEANS OPERABLY CONNECTED IN SAID OUTLET MEANS, MEANS FOR SEPARATILNG UNREACTED AMMONIA FROM REACTANTS, SAID SEPARATING MEANS BEING CONNECTED INTO THE OUTLET OF SAID REACTION VESSEL SUBSEQUENT TO SAILD PRESSURE REDUCING MEANS, MEANS FOR WITHDRAWING THUS SEPARATED AMMONIA, MEANS FOR WITHDRAWING THE REMAINING REACTANTS, MEANS FOR SEPARATING THUS WITHDRAWN REACTANTS INTO ORGANIC PHASE AND WATER PHASE, AN ABSORPTION VESSEL, MEANS FOR INTRODUCING THE WITHDRAWN AMMONIA TO A LOWER SECTION OF SAID ABSORPTION VESSEL, MEANS FOR INTRODUCING WATER FROM SAID WATER PHASE TO AN UPPER SECTION OF SAID ABSORPTION VESSEL, MEANS FOR DETECTING THE LIQUID LEVEL IN SAID ABSORPTION VESSEL, MEANS FOR CONTROLLING FLOW OF WATER TO SAID MEANS FOR INTRODUCING WATER TO SAID UPPER SECTION OF THE ABSORPTION VESSEL, SAID CONTROL MEANS BEING OPERABLY CONNECTED TO SAID LEVEL DETECTING MEANS AND RESPONSIVE TO CHANGES IN LIQUID LEVEL IN SAID ABSORPTION VESSEL, CIRCULATING MEANS FOR WITHDRAWING LIQUID FROM BOTTOM SECTION AND INTRODUCING IT INTO TOP SECTION OF SAID ABSORPTION VESSEL, MEANS FOR REGULAR- 